Refactor message bus and lobby networking flow

* Add local message bus emission with optional argument expansion
* Improve message type validation and callback dispatch
* Simplify lobby match join/disconnect handling
* Move lobby server networking toward an overridable `ServerNetworking` base class
* Update lobby scene to use the dedicated lobby server script
* Remove obsolete window configuration and unused RPC stubs

scripts/server_networking.gd

@@ -1,4 +1,4 @@
-extends Node
+class_name ServerNetworking extends Node
 
 
 var peer: ENetMultiplayerPeer
@@ -44,8 +44,8 @@ func close_connection() -> void:
 	peer.close()
 	peer = null
 
-func server_client_connected(id: int) -> void:
-	Globals.lobby_data.server_client_connected(id)
+func server_client_connected(_id: int) -> void:
+	assert(false, "This method needs to be overridden...")
 
-func server_client_disconnected(id: int) -> void:
-	Globals.lobby_data.server_client_disconnected(id)
+func server_client_disconnected(_id: int) -> void:
+	assert(false, "This method needs to be overridden...")